Sarah Butler switched to a four-day working week at the sixth-form college where she teaches while she was studying for her master's. She intended to make the cut in working hours – and pay – for a year, but has now dropped to two-and-a-half working days since having her son, Indie. She says she will never go back to a five-day week. "There is no amount of money you can put on having that extra day off," she says. "I was trying to do way too much before."

How hard will your finances really be hit?

Undoubtedly, the biggest single question facing anyone thinking of dropping a day (or more) at work is, can you afford the resulting 20% pay cut? For a lot of people the drop in salary will be too much, but for others, especially those who would see their childcare and commuting bills drop, the salary cut can work out better than expected.

A cut in salary may mean you become eligible for child benefit, which is gradually removed when one person in the household earns more than £50,000 a year. You may also be entitled to working tax credits.

"The financial implications were manageable," says Jack Currie, a secondary school teacher who in 2010 dropped from five days to four. "My wife works, so when I went to four days the financial drop was not disastrous – less than 10% of our combined after-tax income." The couple saved one day's childcare costs and the change meant that they qualified for child benefit.

"And, of course, the tax take on the last 20% of your income is higher than on the first 20%, so the loss was 20% of my gross salary, but not 20% of my net take-home pay," says Currie. "The loss to disposable income once the savings, benefits and income reduction were worked out, was £200 to £300 per month. Not meaningless by any means, and if we'd been on one income, that could have been a show-stopper."

Self-employed people might not experience a pay cut at all when moving from five to four days a week, depending on the nature of their business and how well established it is, says independent financial adviser Martin Bamford, of Informed Choice. "A day a week spent outside a business can be extremely valuable for strategic and creative thinking, leading to better results when you are back in the office or sitting in front of clients."

Will your pension and work benefits be affected?

If you are reducing your working hours and therefore pay, you will also take a corresponding cut in the amount being paid into any workplace pension scheme.

"People who reduce their working week will have less disposable income so are potentially less able to consider saving and investments," says Patrick Connolly, an independent financial adviser at Chase de Vere. "However, a decrease in contributions to your pension will have the knock-on effect of taking longer to build an adequate pot for your retirement – so you do need to look at this and whether you can do anything about it."

Connolly suggests first getting a written projection from your company pension provider, which he says is important to look at in today's terms with inflation taken into account.

"The most logical thing to then do is to increase your contributions into that pension fund if you need to, rather than start up a separate personal pension. This is, of course, only if you can afford it," he says.

Other things that may be affected could be any life insurance or income-protection insurance you get from your employer. As these are based on multiples of your salary, the amount that would be paid out will reduce.

The fact that you are working part-time doesn't mean you should be treated less favourably than your colleagues. Your rights are the same and you should still receive the same benefits, such as bonuses, performance-related pay, car parking, childcare provision, healthcare and so on.

What about travel costs?

If you commute to work, either by car or train, then doing so less will save you money. If you drive, cutting your working week will save you petrol, and might reduce your car insurance costs, too, if you can declare a lower annual mileage when applying for a policy.

At the moment, one of the only ways to reduce peak-time rail fares is to pay by carnet tickets, which typically give you 10 journeys for the price of nine and are valid for three to six months. Train companies do not always advertise these, however, so it is worth calling the company that operates your train line to ask whether your route is eligible.

Another option, open to some, is to alter your times of travel. "I do 20 hours' work spread over three days, so I start work at 10.45 now instead of 9am," says Butler. "As I commute to London from Kent that has saved me a considerable amount of money."

What will your employer say when you ask to work less?

The good news for those wanting to drop a day of work is that the rules on the right to request flexible working changed last week, meaning that now anyone is entitled to apply. The right had only been awarded to carers, or people who look after children, but from last Monday it was extended to all employees – even if you want to take time off to, say, walk the dog.

Employers can turn down a request on any of eight grounds, however, and this includes arguing that the change would impact on the business's customer base or that it would add additional costs to the business.

WHEN LESS CAN BE MORE

'Every minute is valuable': Ryan Carson of Florida-based technology education company Treehouse is a convert to the four-day week.

"I responded angrily at first, as I already felt like I didn't have enough time to complete all my tasks. Working less would just make it worse," says Carson. "However, something sparked inside me that wanted to prove the conventional wisdom wrong – that you have to work long, hard hours to create a successful company."

A day later, the couple (then the company's only staff) decided to take every Friday off. Two years later, they hired their first employee and made the four-day week company policy. "We would pay full salaries, offer great benefits, 18 paid days of holiday and yet only work 32 hours a week," says Carson. The company now has 72 full-time employees and is set to earn more than $15m (£8.75m) in revenue this year.

Carson believes the system works because he, and co-founder Alan Johnson, trust their employees. "We see people taking that trust and doing amazing things, not abusing it. It massively increases retention – where else can you go and get 50% more free time with your loved ones?"

One thing that may be surprising for a technology company is that email is banned internally at Treehouse, "because it is a huge time-suck" – tools like forums are used instead.

"The week is intense because you have to work very efficiently to get all your work done," says Carson. "There isn't that feeling of taking a long lunch on a Friday and tuning out. Every minute is valuable."